D»0 COMPOSITION or POTATOES. 



quality in the soil or manure is this difference in composition produced ? 

 In regard to lime the evidence is contradictory. Gypsum may render 

 them harder since legmnin contains sulphur, and a portion of the effect 

 of gypsum upon leguminous crops is supposed to .arise from its yielding 

 sulphur to the growing plants, and thus promoting the production of le- 

 gumin. "Wet and clay lands also favour the production of legumin 

 more than that of starch — but in what way, we are not yet in possession 

 of experimental results of sufficient accuracy to enable us to say. 



§ 21. Of the composition of potatoes, and the effect of circumstances in 

 modifying their composition. 



1°. Composition of potatoes. — Potatoes, in addition to much water, 

 consist of starch, gum, woody fibre, and albumen. The proportions of 

 these several constituents are very variable. Thus, according to 

 Einhof and Lampadius, the following kinds of potatoe consisted in 100 

 parts of — 



2°. Influence of the state of ripeness. — According to Korte the quan- 

 tity of dry solid matter contained in the potatoe depends very much upon 

 the state of ripeness to which it has attained. The ripest leave 30 to 32 

 per cent, of dry matter, the least ripe only 24 per cent. The per 

 centage of starch varies from 8 to 16 per cent. The mean result of his 

 examination of 55 varieties of potatoe gave him for the solid matter 24-9, 

 and for the starch 11*85 per cent. [Schiibler, Agricuhur Chemie, ii., p. 

 213.] 



3°. Influence of variety. — Much appears also to depend upon the 

 variety of potatoe. Thus the following varieties of potatoe grown at 

 Barrochan in Renfrewshire, in 1842, yielded respectively — 



Connaught cups .... 21 per cent, of starch. 



Irish blacks IGg- *' 



White dons 13 " 



Red dons 10| 



— while, according to a starch manufacturer in the neighbourhood, 11^ 

 per cent, has been the average quantity obtained from the common 

 rough red of good quality during the last four years. 



The difference in the quantity of starch yielded by the above-named 

 varieties is the more striking when taken in connection with the weight 

 of each per acre, raised from the same land, treated in the same way. 

 These weights were as follows : — 



So that, of these three crops, that of cups, which weighed the least, 

 gave the largest produce of starch. It yielded nearly twice as much as 

 the red dons, which were half a ton heavier, and one-fifth more than 

 even the white dons, the crop of which was greater by five tons an acre. 

 Such differences as these, in the relative quantities of starch, which may 

 be obtained from an acre of the same land by the growth of different va- 

 rieties of potatoe are deserving of the attentive consideration of the prac- 

 tical man. 



See Appendix, p. 61. 



